Ultrafast dynamics and excited state spectra of open-chain carotenoids at room and low temperatures.

Ultrafast dynamics and excited state spectra of open-chain carotenoids at room and low temperatures. Research Abstract Details 

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Ultrafast dynamics and excited state spectra of open-chain carotenoids at room and low temperatures. Abstract Text:

Dariusz Niedzwiedzki,Jeremy F Koscielecki,Hong Cong,James O Sullivan,George N Gibson,Robert R Birge,Harry A Frank,

Many of the spectroscopic features and photophysical properties of carotenoids are explained using a three-state model in which the strong visible absorption of the molecules is associated with an S0 (1(1)Ag-) --> S2 (1(1)Bu+) transition, and the lowest lying singlet state, S1 (2(1)Ag-), is a state into which absorption from the ground state is forbidden by symmetry. However, semiempirical and ab initio quantum calculations have suggested additional excited singlet states may lie either between or in the vicinity of S1 (2(1)Ag-) and S2 (1(1)Bu+), and some ultrafast spectroscopic studies have reported evidence for these states. One such state, denoted S*, has been implicated as an intermediate in the depopulation of S2 (1(1)Bu+) and as a pathway for the formation of carotenoid triplet states in light-harvesting complexes. In this work, we present the results of an ultrafast, time-resolved spectroscopic investigation of a series of open-chain carotenoids derived from photosynthetic bacteria and systematically increasing in their number of pi-electron carbon-carbon double bonds (n). The molecules are neurosporene (n = 9), spheroidene (n = 10), rhodopin glucoside (n = 11), rhodovibrin (n = 12), and spirilloxanthin (n = 13). The molecules were studied in acetone and CS2 solvents at room temperature. These experiments explore the effect of solvent polarity and polarizability on the spectroscopic and kinetic behavior of the molecules. The molecules were also studied in ether/isopentane/ethanol (EPA) glasses at 77 K, in which the spectral resolution is greatly enhanced. Analysis of the data using global fitting techniques has revealed the ultrafast dynamics of the excited states and spectral changes associated with their decay, including spectroscopic features not previously reported. The data are consistent with S* being identified with a twisted conformational structure, the yield of which is increased in molecules having longer pi-electron conjugations. In particular, for the longest molecule in the series, spirilloxanthin, the experiments and a detailed quantum computational analysis reveal the presence of two S* states associated with relaxed S1 (2(1)Ag-) conformations involving nearly planar 6-s-cis and 6-s-trans geometries. We propose that in polar solvents, the ground state of spirilloxanthin takes on a corkscrew conformation that generates a net solute dipole moment while decreasing the cavity formation energy. Upon excitation and relaxation into the S1 (2(1)Ag-) state, the polyene unravels and flattens into a more planar geometry with comparable populations of 6-s-trans and 6-s-cis conformations.

Ultrafast dynamics and excited state spectra of open-chain carotenoids at room and low temperatures. Publishing Authors By Initials

D Niedzwiedzki,JF Koscielecki,H Cong,JO Sullivan,GN Gibson,RR Birge,HA Frank,

For similar organic chemicals: hydrocarbons: hydrocarbons, acyclic: alkenes: polyenes: carotenoids: xanthophylls research abstracts see: organic chemicals: hydrocarbons: hydrocarbons, acyclic: alkenes: polyenes: carotenoids: xanthophylls research

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MEDLINE DATE:

Ultrafast dynamics and excited state spectra of open-chain carotenoids at room and low temperatures. Journal Published:

PUBLICATION TYPE: Research Support, U.S. Gov't,

Journal: The journal of physical chemistry. B

VOLUME: 111

Page Numbers: 5984-98

Journal Abbreviation:

ISSN: 1520-6106

DAY: 19

MONTH: 04

YEAR: 2007

Ultrafast dynamics and excited state spectra of open-chain carotenoids at room and low temperatures. Information

Number of References:

LANGUAGE: eng

NlmUniqueID: 101157530

Ultrafast dynamics and excited state spectra of open-chain carotenoids at room and low temperatures. Keywords Mesh Terms:

KEYWORDS: Xanthophylls

MESH TERMS: isolation & purification

Chemical & Substance for Abstract: Ultrafast dynamics and excited state spectra of open-chain carotenoids at room and low temperatures. Information

Substance Name: neurosporene

Registry Number: 502-64-7

Grant and Affiliation Information for Ultrafast dynamics and excited state spectra of open-chain carotenoids at room and low temperatures.

AFFILIATION: Department of Chemistry, University of Connecticut, Storrs, Connecticut 06269-3060, USA.

Country: United States

AGENCY: United States NIGMS

GRANT: GM-34548

ACRONYM: GM

MEDLINETA: J Phys Chem B

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